Royal Microscopical Socieiij. 219 



superficial. It resembles Amphiprora iu the f. v., but the absence of 

 the sigmoid keel and central nodule distinguishes it from that genus. 



I have detected two or three other species in the Colon and 

 Campeche dredgings, which I hope to describe in a future paper. 



Nitzschia grandis, n. sp., F. K. — Frustule Knear, ends rounded, 

 valve linear, suddenly tapering to the acute and incurved extremi- 

 ties, keel subcentral, costate punctate between the costae, remainder 

 of valve marked with distinct moniliform striae in transverse series. 

 Costs? 10 in -001, strife 25 in -001 ; length from -0100" to -0200". 

 Navy Bay, Colon, Panama. PI. LXXXIL, Fig. 5, valve; 6, outline 

 of frustule, shaded portion the cingulum ; the dotted line shows 

 ventral margin of lower valve. 



This form is perhaps one of the finest of the genus, and I know 

 of no species with which it is hkely to be confounded. N. Bright- 

 wellii equals it in size, but differs in the position of the keel and 

 also in the striation. 



Triceratium favus, var. sept-angulatum, F. K. — Valve large 

 with seven shghtly concave margins, processes produced, cells hexa- 

 gonal somewhat irregular in size, centre of valve turgid, marginal 

 cells elongated, margin with large moniliform granules, inner surface 

 of valve punctato-striate, radiant, about 20 in '001 ; extreme breadth 

 of valve • 0200". PI. LXXXIl., Figs. 7 and 8. Navy Bay, Colon, 

 Panama. 



I have little hesitation in referring this magnificent form to 

 the above-named species, the number of sides, like the number of 

 nodules on Eupodiscus or Aulacodiscus, being of no specific value. 



All forms of Triceratia with conspicuous hexagonal cells are, I 

 believe, only varieties of T. favus. The radiating punctae on the 

 inner surface are not always present, and are really not on the 

 inner surface of the valve ; they indicate the presence of a thin 

 silicious film, possibly the rudiment of a new valve ; if a valve is 

 crushed between the slide and cover, fragments of the film are 

 detached. 



In the first volume of the ' Lens,' a good Woodbury-type 

 of T. fimhriatum (from a photograph of Dr. J. J. Woodward's) 

 will be found, in which the punct» are very distinctly shown. 

 T. Jimbriatum is rightly referred by Ealfs to T. favus. 



Dr. M. Edwards (' Lens,' vol. ii., p. 105) mentions a six-sided 

 form which agrees very well with my seven-angled variety, and 

 which he calls T. ponderosum, but from the absence of any spe- 

 cific characters I am unable to decide upon their identity with 

 certainty.* I have given the breadth of my largest specimen, the 

 smallest I have seen measured about •0120"; size is, however, of 

 little or no value, even if this form had occurred in sufficient quan- 



* His specimens were found in the Monterey deposit, in which he said a three- 

 sided valve was also detected. 



